The present invention relates to a radio communication apparatus in which a transmission antenna is selected by a diversity transmission system.
In the field of mobile communications, a diversity technique is used to prevent degradation of communication quality due to phasing, etc. An example of the diversity technique is a diversity transmission system adopted in a base station of PHS (personal Handyphone System).
In the diversity transmission system, a plurality of antennas are provided and a transmission signal from a mobile station (radio communication terminal) is received by the plural antennas. On the basis of reception results by the plural antennas, an antenna with highest communication quality is found and a signal is transmitted to the mobile station from this antenna. This system is advantageous in that since the antenna is selected on the basis of the degree of phasing at antenna, there is no load on the mobile station side.
However, if the diversity transmission system is applied to base station equipment of a mobile communication unit of a multi-channel access system such as CDMA (Code Division Multiple Access), the following drawback will arise. In the case of CDMA, an up link from a mobile station to a base station is easily interfered with by another channel. If communication quality of all propagation paths is degraded by such interference, detection precision of parameters indicating communication quality of each path also deteriorates and the selected antenna is not necessarily the best one.
In order to prevent this problem, it is possible to reduce the influence of interference by decreasing the number of multiplexed channels. With this method, however, a new problem arises in that the efficiency of radio resource use such as frequency will also decrease.
As described above, when multi-channel communication is performed in the conventional radio. communication apparatus of diversity transmission system, if the communication quality of all communication paths deteriorates due to inter-channel interference, the best antenna will not necessarily be selected for communication.
The present invention has been made in order to solve this problem, and its object is to provide a radio communication apparatus capable of selecting the best antenna and enhance communication quality without lowering the efficiency of use of frequency.
In a radio communication apparatus having a diversity transmission function according to the present invention, a signal in which plural channels are multiplexed is received via a plurality of paths, a best path is selected, and signals are transmitted via the selected path. The apparatus comprises transmitters, the number of which is greater than the number of the multiplexed channels, and means for transmitting transmission signals of some channels via the plural transmitters and the plural paths.
Since the transmission signal of a certain channel is transmitted via plural transmitters and paths, the possibility of erroneous selection of paths is decreased. As a result, the communication quality can be enhanced. Further, when a great number of channels are multiplexed, an up link will easily interfere with another channel. In the prior art, in order to prevent erroneous selection of paths, the number of channels to be multiplexed is reduced and the frequency use efficiency is decreased. According to the present invention, the diversity transmission control can be performed without decreasing the frequency use. efficiency.